Re: [Pyparsing] Index operator

[Paul M. <pt...@au...>]

Are you using operatorPrecedence?  If so, then expand the definition of the
operand expression that you are passing in to handle the optional indexing.
As Ralph Corderoy already pointed out, your index is probably going to be
another arithmetic expression, so you will need to define operand in terms
of the expression that will be defined using operand -> the arithmetic
expression will have to be defined as a Forward.  Something like this:

    arith_expr = Forward()
    operand = number | variable+Optional('[' + arith_expr + ']')
    arith_expr << operatorPrecedence(operand,
        [
        ... operator definitions go here ...
        ])

If your evaluator does not use operatorPrecedence, but you have done your
own grammar expansion, you'll have to reinterpret this suggestion in the
context of your own grammar structure.

-- Paul


-----Original Message-----
From: Will McGugan [mailto:wil...@gm...] 
Sent: Sunday, September 25, 2011 7:30 AM
To: Pyp...@li...
Subject: [Pyparsing] Index operator

Hi,

I have a custom expression evaluator that is working quite well, bit I'd
like to implement an operator that works just like indexing a string or
sequence in python.

i.e. something[<expression>]

I can't quite figure out how to do this. Can anyone give me any pointers?

Thanks,

Will McGugan

-- 
Will McGugan
http://www.willmcgugan.com
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